This invention relates to wastewater treatment, and in particular, to an underdrain assembly for supporting filter media and providing means for air flow to move through the filter media.
It is desirable to provide wastewater filtration units with means, such as underdrains, for providing even distribution of liquid and gas during filter backwashing operations and the uniform collection of filtered water during the normal operation of filtration units. It is also desirable to provide supporting means for the filter media such that the filter media is spaced apart from the bottom of the filtration unit. This provides a space for the pipes which comprise a portion of the water and air distribution system which is situated below the filter media. It also physically separates the filter media from the water and air distribution pipes. This helps prevent clogging of the orifices in the pipes by the finer particles of the filter media as well as removing the weight load of the overlying filter media from the pipes. Prior art underdrains are generally made from stainless steel. This is expensive.